Friday, February 28, 2014

Gavin A. Schmidt, Drew T. Shindell & Kostas Tsigaridis have a new article in Nature Geoscience (open access). What they've done is estimate the impact of actual measures of solar, volcanoes and ENSO on a CMIP5 ensemble. They found that this reduced the recent difference between models and observations a whole lot.

What they found in particular was the the models most likely overestimated the cooling from the Pinatubo eruption in the 1990s, making the models too cool and, when observed solar radiation, volcanic eruptions and ENSO were factored, in the models are pretty close to observations.

Here is the figure from the paper. Click to enlarge it.

Figure 1: Updated external influences on climate and their impact on the CMIP5 model runs.a, The latest reconstructions of optical depth for volcanic aerosols9, 10 from the Mount Pinatubo eruption in 1991 suggest that the cooling effect of the eruption (1991–1993) was overestimated in the CMIP5 runs, making the simulated temperatures too cool. From about 1998 onwards, however, the cooling effects of solar activity (red), human-made tropospheric aerosols (green) and volcanic eruptions (pink) were all underestimated. WMGHG, well-mixed greenhouse gases.b, Global mean surface temperature anomalies, with respect to 1980–1999, in the CMIP5 ensemble (mean: solid blue line; pale blue shading: 5–95% spread of simulations) on average exceeded two independent reconstructions from observations (GISTEMP Land–Ocean Temperature Index (LOTI)6, solid red; HadCRUT4 with spatial infilling7, dashed red) from about 1998. Adjusting for the phase of ENSO by regressing the observed temperature against the ENSO index11 adds interannual variability to the CMIP5 ensemble mean (dashed blue), and adjusting for updated external influences as in a further reduces the discrepancy between model and data from 1998 (black). The adjusted ensemble spread (dashed grey) clearly shows the decadal impact of the updated drivers. As an aside, we note that although it is convenient to use the CMIP5 ensemble to assess expected spreads in possible trends, the ensemble is not a true probabilistic sample.

It's going to get hotter

We conclude that use of the latest information on external influences on the climate system and adjusting for internal variability associated with ENSO can almost completely reconcile the trends in global mean surface temperature in CMIP5 models and observations. Nevertheless, attributing climate trends over relatively short periods, such as 10 to 15 years, will always be problematic, and it is inherently unsatisfying to find model–data agreement only with the benefit of hindsight. We see no indication, however, that transient climate response is systematically overestimated in the CMIP5 climate models as has been speculated, or that decadal variability across the ensemble of models is systematically underestimated, although at least some individual models probably fall short in this respect.

Most importantly, our analysis implies that significant warming trends are likely to resume, because the dominant long-term warming effect of well-mixed greenhouse gases continues to rise. Asian pollution levels are likely to stabilize and perhaps decrease, although lower solar activity may persist and volcanic eruptions are unpredictable. ENSO will eventually move back into a positive phase and the simultaneous coincidence of multiple cooling effects will cease. Further warming is very likely to be the result.

Anthony Watts hasn't picked up on this paper yet, but I expect he will sooner or later.

“Here we argue that a combination of factors, by coincidence, conspired to dampen warming trends in the real world after about 1992. CMIP5 model simulations were based on historical estimates of external influences on the climate only to 2000 or 2005, and used scenarios (Representative Concentration Pathways, or RCPs) thereafter4. Any recent improvements in these estimates or updates to the present day were not taken into account in these simulations.”

But rather than question the viability of the models, he blames nature for not playing the game,

“We conclude that use of the latest information on external influences on the climate system and adjusting for internal variability associated with ENSO can almost completely reconcile the trends in global mean surface temperature in CMIP5 models and observations.”

But rather than question the viability of the models, he blames nature for not playing the gameBut nature still has to obey the laws of physics, or - at least - we still think that nature obeys the laws of physics. If you were able to show that it does not obey the currently known laws of physics, that would be amazing. Otherwise, trying to reconcile why the results from climate models are not quite what was observed is typically called "doing science".

Of course there is a lot of "settled science". For example, it's accepted as "settled" that CO2 is a greenhouse gas.

I'd say Anonymous has well and truly "settled" any doubt that Anonymous is an ordinary run-of-the-mill climate science denier liar, quite possible of the "climate science is a hoax" type - but that bit may not be quite settled yet.

Looks to me like Gavin Schmidt actually showing the models are really, really good. The models work fine with real-world data.

The one problem we have is that we don't know for sure how the sun and volcanoes (and ENSO) will behave over short time-scales. Perhaps anonymous is one of those who wants the world to gamble that the sun will not only remain as 'quiet' as it is today, it actually should become more 'quiet', that volcanoes become more active, and that ENSO magically remains in a "mostly La Nina" state.

I think Anonymous is saying that the CMIP5 models failed to use the actual future data for volcanoes, ENSO, etc. rather than use average behaviour to project ahead. Scientists inability to see the future in sufficient detail means, in Anon's opinion, that models must inevitably fail. Which is no doubt a great comfort to him/her, given what the models project.

Real outcomes lie within CMIP5 projections, but that's easily enough ignored, I'm sure, by those who have a talent for ignorance.

Certainly one could consider the possibility that most of what we know about atmospheric physics is drastically mistaken due to some yet unknown science, and thus "question the viability of the models", but there really isn't any evidence pointing in that direction.

A much more likely explanation is that fine-tuning the models, as Gavin suggests, incorporating actual ENSO events and more accurate temperature and aerosol data, brings the projections more in line with observations.

It's certainly a learning opportunity, and models are a learning tool. It's where discrepencies occur that you're missing something and should focus your attention.

"The models have failed" has been a refrain from the moment they were first developed; as I recall Pat Michaels lied to Congress about them in 1998. On the day Hansen personally sabotaged the Capitol Hill air-conditioning system (it's true, I read it on the internet).

Models are a work in progress, but any honest and objective evaluation of their performance reveals that they are performing their design function well. This being the investigation of long-term climate behaviour under various different forcing scenarios.

Deniers - like you, Anon. - lie and misrepresent so continuously that they forget that they are even doing it. They forget that the claims that the models are "falsified" are based on faked-up graphs by other liars further up the food chain. They forget that models are not designed to predict Earth's climate accurately, year by year or even by decade, but to provide an understanding of multi-decadal forced response.

Deniers - like you, Anon. - lie about other things too, for example that we can make informative estimates of TCR (let alone ECS) based on a decade of climate behaviour. They pretend that warming is supposed to be monotonic, when no climate scientist or modeller has ever said such a thing. They pretend that natural variability should simply have ceased, but this is absurd. They do all this an much more besides.

Then, to ice the cake, they pop up all over the internet posting incoherent, mangled, dishonest misrepresentations of the science, just as you have done here.

I read Gavin's paper and don't see where the volcanic aerosols are coming from.

It is much more straightforward to model the pause by the strong compensating effects of ENSO -- just use the SOI as a proxy -- along with other cyclic thermodynamic factors. These can be pulled out and their effects calibrated from the longer 130+ year time series; this unfortunately is not yet an accepted way of analysis.

I feel that this turn of events has the makings of an impasse. I noticed that Wonderin Willis has a guest post at WUWT where he dismisses the idea of volcanic aerosols on global temperature, which is completely misguided. Yet he did also note that the volcanic aerosol measurements have been flat recently. That's what happens when someone takes a shotgun approach, they will occasionally hit a target.

I use the GISS aerosol forcing table maintained by Sato for my own analysis, and can't see where the aerosol concentration is coming from, as it looks flat ever since Pinatubo settled down. If someone has any insight on this, I would be grateful for suggestions.

...Here we present a detailed analysis of the impact of recent volcanic forcing on tropospheric temperature, based on observations as well as climate model simulations. We identify statistically significant correlations between observations of stratospheric aerosol optical depth and satellite-based estimates of both tropospheric temperature and short-wave fluxes at the top of the atmosphere. We show that climate model simulations without the effects of early twenty-first-century volcanic eruptions overestimate the tropospheric warming observed since 1998. In two simulations with more realistic volcanic influences following the 1991 Pinatubo eruption, differences between simulated and observed tropospheric temperature trends over the period 1998 to 2012 are up to 15% smaller, with large uncertainties in the magnitude of the effect....

I wouldn't be surprised if that was the work that Gavin Schmidt used, especially as he cited it in his own article.

The Santer paper is behind a paywall and I'm not a subscriber to Nature Geoscience. However you can download the supplementary information, which has a lot of info. It refers to a observations of stratospheric aerosol optical depth, among other things:

I remember that the response to Penatubo has been used to estimate climate sensitivity and that it gave a high consensus answer. If as alleged in this paper, the forcing used in that calculation is wrong, someone should redo the calculation.

Tightening up Pinatubo cooling estimates won't change the central estimates for TCR or ECS. Look at the paper again: with improved (reduced) estimates for negative aerosol forcing from Pinatubo, observations and models come into closer agreement. Which means that modelled estimates of TCR and ECS are validated. So far, so mainstream.

Give up the pseudoscepticism and learn about climate science instead. It is a far better use of your time.

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All you need to know about WUWT

WUWT insider Willis Eschenbach tells you all you need to know about Anthony Watts and his blog, WattsUpWithThat (WUWT). As part of his scathing commentary, Wondering Willis accuses Anthony Watts of being clueless about the blog articles he posts. To paraphrase:

Even if Anthony had a year to analyze and dissect each piece...(he couldn't tell if it would)... stand the harsh light of public exposure.

Definition of Denier (Oxford): A person who denies something, especially someone who refuses to admit the truth of a concept or proposition that is supported by the majority of scientific or historical evidence.
‘a prominent denier of global warming’
‘a climate change denier’

Alternative definition: A former French coin, equal to one twelfth of a Sou, which was withdrawn in the 19th century. Oxford. (The denier has since resurfaced with reduced value.)